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Fri, 22 Jan 2021 09:39:51 +0100 (CET) From: Markus Armbruster To: Paolo Bonzini Subject: Re: [PATCH 04/25] keyval: accept escaped commas in implied option References: <20210118163113.780171-1-pbonzini@redhat.com> <20210118163113.780171-5-pbonzini@redhat.com> Date: Fri, 22 Jan 2021 09:39:51 +0100 In-Reply-To: <20210118163113.780171-5-pbonzini@redhat.com> (Paolo Bonzini's message of "Mon, 18 Jan 2021 11:30:52 -0500") Message-ID: <87mtx1cqlk.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=63.128.21.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.168, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, imammedo@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Paolo Bonzini writes: [...] > diff --git a/util/keyval.c b/util/keyval.c > index be34928813..eb9b9c55ec 100644 > --- a/util/keyval.c > +++ b/util/keyval.c > @@ -16,8 +16,8 @@ > * key-vals = [ key-val { ',' key-val } [ ',' ] ] > * key-val = key '=' val | help > * key = key-fragment { '.' key-fragment } > - * key-fragment = / [^=,.]+ / > - * val = { / [^,]+ / | ',,' } > + * key-fragment = { / [^=,.] / | ',,' } > + * val = { / [^,] / | ',,' } > * help = 'help' | '?' > * > * Semantics defined by reduction to JSON: > @@ -78,13 +78,13 @@ > * Alternative syntax for use with an implied key: > * > * key-vals = [ key-val-1st { ',' key-val } [ ',' ] ] > - * key-val-1st = val-no-key | key-val > - * val-no-key = / [^=,]+ / - help > + * key-val-1st = (val-no-key - help) | key-val > + * val-no-key = { / [^=,] / | ',,' } I finally remembered why I made val-no-key non-empty: to avoid amiguity. Before the patch, "" can only be parsed as empty key-vals. Results in an empty QDict. Afterwards, the grammar is ambiguous: "" can also be parsed as empty val-no-key, reduced via key-val-1st to non-empty key-vals. Results in a QDict with one entry mapping the implied key to "". I'm a bit concerned I similarly forgot something that made me avoid ',,' escapes in val-no-key. Even if we brushed off the ambiguous grammar issue (and we should not!), desugaring "" into "implied=" feels unwise, and ",k=v" into "implied=,k=v" only slightly less so. Let's keep val-no-key non-empty. Ripple effect... I made val-no-key match key (almost): val-no-key = / [^=,]+ / key = key-fragment { '.' key-fragment } key-fragment = / [^=,.]+ / The only difference is val-no-key accepts consecutive '.'. Commit 8bf12c4f75 "keyval: Parse help options" muddied the waters a bit by adding '- help' to val-no-key. Your commit moves it to key-val-1st (good). It also permits empty key-fragment, and thus consecutive '.' (good because it makes val-no-key match key exactly, but also possibly confusing because key-fragment can't actually be empty due to the "Key-fragments must be valid QAPI names or consist only of decimal digits" condition). Okay. It also changed both val-no-key and key to accept empty. We need to keep *both* non-empty. Your change to val is not wrong, but I prefer the old version, because it's closer to how the code works. > * > * where val-no-key is syntactic sugar for implied-key=val-no-key. > * > - * Note that you can't use the sugared form when the value contains > - * '=' or ','. > + * Note that you can't use the sugared form when the value is empty You can with your grammar change, unless the code doesn't match the grammar. Which would be a bug. > + * or contains '='. > */ [...] I apologize for sitting on this patch for so long. Something felt wrong, but I couldn't put a finger on it. Now I can at least for the empty val-no-key part.